1. Field of the Invention
The present invention relates to apparatus for dispensing material produced by a chemical reaction between a first chemical re-agent and a second chemical re-agent. The dispensed material may be foam-like or elastomeric. Preferably, the material is in a fluid state allowing it to be cast and then cured into a substantially solid construction.
2. Description of the Related Art
Foam-like material such as polyurethane is produced in situ so that it expands and sets into required shapes. A first chemical re-agent may be a diol and a second chemical re-agent may be a diisocyanate. In addition, small amounts of water are added to the reaction mixture during the polymerisation process to produce carbon dioxide gas that acts as the foaming agent.
High pressure systems are known in which the chemical re-agents are brought into contact under high velocity having been released from respective high pressure nozzles. High pressure systems of this type produce good quality polyurethane foam and require minimal maintenance. However, a problem with these systems is that output rates tend to be relatively high and attempts to scale down output production by reducing the size of the apparatus, and thereby reducing the volume of material released from the respective nozzles, have introduced further engineering difficulties.
Low pressure systems are known that use mechanical mixing operations and are thereby capable of operating at lower output rates/volumes. However, low pressure systems introduce further problems in that the quality of the mix tends to be lower than that produced by high pressure systems and organic solvents are required on a regular basis to effect the cleaning of a mixing chamber. In both of these known systems the rate of foam production is controlled by controlling the flow of the individual re-agents.
A further problem may be encountered with existing high pressure systems where injection into a mould is required. If the mould resists flow of material from the mixing head, a consequential build-up of fluid pressures within the system can prove catastrophic to production.